1. Field of the Invention
This invention relates to keyboard input circuitry, and more particularly, to improved keyboard circuitry for use in data processing systems.
2. Description of the Prior Art
Keyboards having a matrix of keys are particularly well suited for use in data processing systems. The keys of such keyboards provide continuity between corresponding column and row conductors when depressed. Output signals from the data processing system are coupled to each column conductor for sequentially scanning the keyboard for depressed keys. A depressed key is sensed when the output signal from the column conductor is present on the corresponding row conductor. Thus, for a matrix of keys having K columns and J rows, the data processing system must provide K output signals for the K columns and monitor the J row conductors. As a result, a relatively large number of signals (K+J) are required to interface the data processing system to the keyboard.
In order to reduce the number of interconnecting signals, additional circuitry may be utilized for scanning the matrix of keys and providing a digitally coded signal when a particular key is depressed. The digitally coded signal uniquely identifies the depressed key. However, the stored program control of the data processing system must be programmed to decode the digitally coded signals in order to recognize the depressed key, and the additional circuitry increases the cost of the data processing system.
For the foregoing and other shortcomings and problems, there has been a long felt need for an improved keyboard input circuitry for use for the data processing system.